The present application relates to reducing voltage ripple of an electric signal. It finds application in the field of imaging modalities, and in particular, to imaging modalities that can employ multi-energy imaging techniques (e.g., where radiation is emitted at a plurality of distinct energy levels). For example, medical, security, and/or industrial applications may utilize a multi-energy (e.g., dual-energy) computed tomography (CT) scanner to discriminate objects based upon a plurality of characteristics (e.g., density, chemical composition (e.g., derived from z-effective information), etc.). It will be appreciated that while the present application finds particular applicability to multi-energy imaging techniques, it may also apply with respect to single-energy imaging techniques and/or to non-imaging applications.
Today, CT and other imaging modalities (e.g., single-photon emission computed tomography (SPECT), mammography, digital radiography, etc.) are useful to provide information, or images, of interior aspects of an object under examination. Generally, the object is exposed to radiation comprising photons (e.g., such as x-rays, gamma rays, etc.), and an image(s) is formed based upon the radiation absorbed and/or attenuated by the interior aspects of the object, or rather an amount of photons that is able to pass through the object. Typically, highly dense aspects of the object (e.g., or aspects of the object having a composition comprised of higher atomic number elements) absorb and/or attenuate more radiation than less dense aspects, and thus an aspect having a higher density (e.g., and/or high atomic number elements), such as a bone or metal, for example, will be apparent when surrounded by less dense aspects, such as muscle or clothing.
Radiographic imaging modalities generally comprise, among other things, one or more radiation sources (e.g., x-ray, gamma-ray, etc.) and a detector array comprised of a plurality of channels that are respectively configured to convert radiation that has traversed the object into signals that may be processed to produce the image(s). Such radiographic imaging modalities may be classified as single energy or multi-energy imaging systems based upon whether the imaging modality is configured to emit radiation at merely one energy level (e.g., or energy spectrum due to slight variations in the energy of emitted photons) or at two or more distinct energy levels (e.g., or two or more distinct energy spectra). Example applications for multi-energy imaging systems include, but are not limited to, bone densitometry, explosive detection, and/or quantitative CT, for example.
Multi-energy imaging systems employ numerous techniques to generate photons at two or more distinguishable energy levels and/or to discriminate between the energy levels of emitted photons when they are detected. One of the more common approaches is known as source switching, where the emitted radiation is alternated between at least two distinguished or different energy levels. Several techniques may be used to implement source switching. For example, in one approach, the voltage applied to a single radiation source is varied causing the emitted radiation's energy to vary with the change in voltage. In another approach, two or more spatially separated sources are configured to alternate radiation emissions (e.g., by alternating power to the sources). Where there are two energy sources, for example, one of the sources may be configured to emit higher energy radiation, while the other may be configured to emit lower energy radiation, for example.
Typically, electrical components that provide for transitioning between two or more voltage levels comprise, among other things, a high voltage power supply (e.g., which may comprise a transformer-rectifier combination) for generating an electric signal comprising a desired voltage and/or modifying an electric signal to comprise the desired voltage (e.g., where the desired voltage may change to alter an energy spectrum of radiation emitted). While the desired output of the power supply would be an electric signal having a constant voltage at a desired level, in practice power supplies (e.g., and in particular high voltage power supplies) often output an electric signal having a voltage that fluctuates within a range of the desired voltage. This is particularly true during a transition between two desired voltages, because the change in output current to support the changed voltage typically lags behind the change in voltage. This fluctuation may be referred to as a voltage ripple and may be undesirable because it may cause emitted photons to deviate (e.g., slightly) from a specific energy level (e.g., be emitted somewhat within an energy spectrum).
To reduce this fluctuation, voltage capacitors that are configured to dampen changes in voltage may be utilized. Typically, higher value capacitors are better at dampening voltage ripples than lower value capacitors. However, higher value capacitors also store more electric charge than lower value capacitors, and thus generally take longer to discharge than lower value capacitors. Thus, high value capacitors may prolong the transition between two or more voltage levels, which is typically undesirable in imaging modalities. It will be appreciated that while high voltage, fast discharging power-supplies do exist, such power-systems are rather expensive making the implementation of such power-systems generally cost prohibitive.
Therefore, it is a desire of this application to describe, among other things, one or more systems and/or techniques for reducing a voltage ripple yielded from an electric signal produced/modified by a power supply (e.g., comprising a high voltage transformer and a rectifier) while using lower value capacitors.